Introduction
Method and system design
System design
Operating conditions | Unit | Weeks of operating | ||||
---|---|---|---|---|---|---|
Period1 (P1) Week 1–9 | Period2 (P2) Week 10–18 | Period3 (P3) Week 19–27 | Period4 (P4) Week 28–36 | Period5 (P5) Week 37–45 | ||
Flow rate | L min−1
| 1 | 3 | 2 | 1 | 1.5 |
Inflow time | h day−1
| 6 | 6 | 3 | 6 | 6 |
Hydraulic loading rate | m day−1
| 0.36 | 1.08 | 0.36 | 0.36 | 0.54 |
Ratio of dry–wet strength | 3 | 3 | 7 | 3 | 3 |
Wastewater properties
Parameters | pH |
T (°C) | COD (mg L−1) | T-N (mg L−1) | NH4
+-N (mg L−1) | NO3
−-N (mg L−1) | NO2
−-N (mg L−1) | Org-N (mg L−1) |
---|---|---|---|---|---|---|---|---|
Inflow | 6.9–7.6 | 14.8–26.3 | 178–504 | 28.9–46.0 | 20.7–39.1 | 2.3–6.2 | 0.01–0.20 | 6.2–13.2 |
Sampling and measurement
Data analysis
Results and discussion
System performance and effect of operating conditions
COD, NH4+-N and T-N
Impact of HLR
Parameters | HLR: 0.36 m day−1
D/W: 3 | HLR: 1.08 m day−1
D/W: 3 | HLR: 0.36 m day−1
D/W: 7 | HLR: 0.54 m day−1
D/W: 3 | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
COD (mg L−1) | T-N (mg L−1) | NH4
+-N (mg L−1) | COD (mg L−1) | T-N (mg L−1) | NH4
+-N (mg L−1) | COD (mg L−1) | T-N (mg L−1) | NH4
+-N (mg L−1) | COD (mg L−1) | T-N (mg L−1) | NH4
+-N (mg L−1) | |
Inflow | 144–504 | 22.6–40.9 | 16.7–37.5 | 177–400 | 29.3–46.0 | 25.6–39.1 | 163–340 | 29.2–39.6 | 18.0–33.9 | 175–385 | 24.5–39.8 | 20.3–35.2 |
ABFa
| 98–200 | 20.8–31.9 | 16.8–30.2 | 48–298 | 21.0–42.9 | 16.6–40.1 | 98–297 | 18.2–41.7 | 13.8–31.1 | 109–245 | 23.6–38.9 | 18.2–33.4 |
TBFa
| 54–148 | 17.8–25.7 | 15.8–24.5 | 26–234 | 25.5–40.5 | 10.5–39.2 | 105–219 | 15.4–44.0 | 7.4–21.2 | 64–149 | 19.8–29.1 | 11.9–28.5 |
BVFIa
| 23–135 | 8.5–16.4 | 2.8–9.0 | 8–79 | 18.0–32.3 | 3.8–22.5 | 32–58 | 14.8–24.7 | 0.7–17.3 | 23–98 | 9.3–17.5 | 3.2–10.5 |
BVFIIa
| 8–32 | 6.0–9.8 | 0.1–1.6 | 7–33 | 19.6–29.5 | 0.5–8.6 | 8–18 | 9.3–17.7 | 0.6–1.8 | 7–35 | 5.4–10.4 | 0.2–1.3 |
Impact of the ratio of dry–wet strength (D/W)
OTR under different operating conditions
Nitrogen speciation and transformation
Nitrogen speciation
Parameters |
T (°C) | pH | COD (mg L−1) | T-N (mg L−1) | NH4
+-N (mg L−1) | NO3
−-N (mg L−1) | NO2
−-N (mg L−1) | Org-N (mg L−1) | δ15N-NO3
−/‰ |
---|---|---|---|---|---|---|---|---|---|
Inflow | 22.3 ± 2.2 | 6.7 ± 0.2 | 236 ± 52 | 36.5 ± 3.7 | 24.5 ± 2.8 | 3.0 ± 1.3 | 0.03 ± 0.06 | 8.9 ± 2.3 | 5.14 ± 0.64 |
ABF | 22.2 ± 2.1 | 6.4 ± 0.4 | 206 ± 55 | 24.9 ± 3.0 | 16.8 ± 1.6 | 1.7 ± 1.1 | 0.01 ± 0.01 | 6.4 ± 1.8 | 5.61 ± 0.51 |
TBF | 22.2 ± 2.3 | 6.8 ± 0.2 | 140 ± 40 | 21.3 ± 3.3 | 13.5 ± 3.1 | 4.4 ± 2.1 | 0.12 ± 0.10 | 3.3 ± 1.1 | 8.81 ± 3.00 |
BVFI | 22.1 ± 2.2 | 7.0 ± 0.2 | 54 ± 20 | 14.9 ± 1.8 | 2.3 ± 0.6 | 11.0 ± 1.8 | 0.01 ± 0.01 | 1.6 ± 0.5 | 10.87 ± 4.54 |
BVFII | 22.1 ± 2.1 | 7.3 ± 0.2 | 14 ± 5 | 10.2 ± 0.9 | 0.7 ± 0.2 | 8.4 ± 0.6 | 0.18 ± 0.12 | 1.0 ± 0.6 | 8.72 ± 2.79 |
Isotope δ15N-NO3−analysis
System stage | NO3
−-N production (Y
prodution) (mg L−1) | NO3
−-N reduction (Y
reduction) (mg L−1) |
---|---|---|
ABF | −0.66 | 0.64 |
TBF | 5.48 | 2.78 |
BVF I | 9.18 | 2.58 |
BVF II | 3.42 | 6.02 |
Crucial factors in T-N removal
Item |
T (E) | pH (E) | COD/T-N (I) | COD/NH4
+-N (I) | COD (E) | T-N (E) | T-N (RE) | T-N (MR) |
---|---|---|---|---|---|---|---|---|
T (Ea) | 1 | |||||||
pH (Ea) | −0.340 | 1 | ||||||
COD/T-N (Ib) | 0.127 | 0.066 | 1 | |||||
COD/NH4
+-N (Ib) | 0.195 | 0.042 | 0.930** | 1 | ||||
COD (Ea) | −0.023 | 0.791* | −0.154 | −0.229 | 1 | |||
T-N (Ea) | −0.095 | −0.248 | −0.733* | −0.743* | −0.125 | 1 | ||
T-N (REc) | 0.517 | 0.089 | 0.734* | 0.795* | 0.008 | −0.845* | 1 | |
T-N (MRd) | 0.679* | −0.045 | 0.731* | 0.648 | −0.121 | −0.652 | 0.953** | 1 |
Conclusion
-
MBV efficiently removed many pollutants, especially nitrogen. Mean NH4 +-N removal was 93.3 % (influent NH4 +-N, 25.3 mg L−1), and mean T-N removal could reach 58.2 % of influent concentration (30.6 mg L−1).
-
The MBV system achieved an HLR of 0.54 m day−1 and maintained a nitrogen removal efficiency of 60–65 %.
-
We tracked the transformation of nitrogen speciation. The isotope δ15N-NO3 − dilution method interpreted the production of and reduction in NO3 −-N. This method also confirmed the occurrence of nitrification and denitrification.
-
Aside from the impact of operating conditions on nitrogen removal, COD/T-N was also a crucial factor.